Cathode-ray beam deflection circuit



March 28, 1950 w. A. STEWART cATHoDE-RAY BEAM DEFLECTION CIRCUIT 4Filed Feb. l2, 1949 -c, /s-HLLou/o Hna/1r FL/nmmem-HL FnaQL/ncy IN1/Emol; A wIlL/Hm fl. .HELL/HRT L, uwen L,

VOLT;

Patentedl Mar. 28, 1,9,.5

UNITED STATES PATENT OFFICE CATHODEHRAY BEAM,DE1`IiE(`/"IYI0N4 oinoUIT William A. Stewart, Philadelphia, Pa., assigner to Philco Corporation, Philadelphia, Pa., a corpo-fifation of Pennsylvania Application February 12, 1949,. Serial No. 76,086

The present invention relates to cathode ray beam deflection circuits, and more particularly relates to those circuits which are designed to form part of a television system wherein .the electron scanning beam of a cathode ray tube is deflected in at least one of its mutually pei-pendicular directions by the action of an electrostatic field.

Television systems employing cathode ray tubes of the type having two pairs of electrostatic denection plates commonly include means for generating two sawtooth voltage variations having dinerent repetition frequencies. In certain known arrangements, these sawtooth voltages are respectively applied to one denecting plate of each pair, while the remaining plates are maintained at ground or some other constant potential. In other known arrangements, however, two further sawtooth voltages are developed which are in phase opposition to the voltages in itially generated. These additional voltages are also applied'to the defiecting plates in a manner such that the cyclically varying' potentials on the two plates of each pair areY symmetrical, or balanced, with' respect to a predetermined voltage level. The provisionY of such balancedv voltages is usually desirable, inasmuch as it increases the angle through which the cathode ray beam may be denected and hence the size of the image raster area scanned by the beam. In addition, by causing the balanced voltages to have a reference level which coincides substantially with the second anode potential of the cathode ray tube, any defocusing of thefcathode ray scanning beam (which frequently results when a so-called "single-ended deflecting circuit is used) is largely overcome. y

In one form of electrostatic deflecting arrange ment particularly adapted for usein television receivers, an electron discharge tube 4is provided with a time constant circuit connected toits anode and a further time constant circuit connected to -its cathode. Each of these timeconstant circuits customarily includes a condenser, or other energy-storage device, which is discharged by conduction of the-tube and* charged duringthe time that the` tube is cut. oil. By selecting proper values ofresistance in the charging path of each condenser, thevoltage developed in the anode circuit of the tube .duringscansion will be alinearly rising sawtooth, while the`voltage appearing-in the cathode. circuit will' bea linearly falling sawtooth.' Furthermore;v these 7 Claims. (Cl. S15-*26) voltages will be balanced with respect to one an" other. A system operating in accordance with the above principles is described in a nited States patent to C. E. Hallmark, No. 2,345,668; issued April 4,1944.

One disadvantage in such an arrangement, however, resides in the fact that the charges which are developed on the condensers in the -respective time constant circuits have peak-to-peak values which are lower than the voltage of the operating potential source itself. In fact, the peak=topeak value of these developed charges must be considerably below the voltage supplied to the anode of the discharge tube during scan sion if approximate linearity of deflection is de- Vsired. Thus the angle through which the cathode ray beam is deflected may be limited to such a degree that the circuit is rendered unsuitable for use in manytypes of television systems. In order to overcome this disadvantage, it has been the procedure in certain cases to step up the voltage of the operating potential source, but, since this usually requires additional componentsi it may serve' to increase the overall cost of the telei.

vision apparatus.

-Another type of presently employed deiection circuitis one in which the sawtootlf'lvoltage-generating network is arranged as a separate unit so that it merely providesthe control, or driving; voltage for a power tube. The latter elementiin this case forms part of the circuit which actually supplies sawtooth energy to the deflecting plates. As a consequence, a relatively high scanning volt age output may be obtained relative to the amplis tude of the voltage which appears on the control electrode of the power tube. It is obvious, however, that this arrangement is considerably more complex than one in which the output of the: saw= tooth generator is applied directly to the plates ofthe cathode ray tube itself, inasmuch as the latter circuit provides a deflecting voltage which is utilized directly for beam deflection without the: presence of'an intervening amplifier stage.

According. to one feature of the present inven tion, a single-tube cathode ray beam deflection circuit of the electrostatictype is providedA in which a pair of parallel-tuned, or parallelereso'-1 naht, inductance-capacitance networks are rei,- spectvely connected in the anode and. cathode circuits of an electron discharge tube. By properly determining the natural periodofoscillation of these resonant networks, it has been found thatthe energy developed acrossrthe inductive riods of the cathode ray beam (when the discharge tube is conductive) may be utilized for the purpose of increasing the charge which appears on the capacitive portion of each network during scansion. The peak-to-peak value of this charge may accordingly be raised to a point considerably in excess of that which would normally be reached as a result of charging the capacitor from the operating potential source alone. Furthermore, by a particular connection of these parallel-resonant networks, both with respect to each other and with respect to the electron discharge tube, it has been found that the waveforms of the voltages respectively appearing on the capacitive portions of` the networks may be made substantially symmetrical about a xed reference level.

In accordance with a further feature of the present invention, a plurality of wave-'shaping units are provided by means of which any dissimilarity between the voltages respectively developed across the two resonant networks may be corrected. Furthermore, this is accomplished without increasing the distributed capacity in the circuit to an objectionable degree, and without appreciably increasing that portion of each deection cycle which is allotted for the retrace action of the cathode ray scanning beam.

In accordance with an additional feature of the invention, the balanced deflecting voltages which are developed in the manner above set forth are capacitively coupled to the deecting plates of the cathode ray tube. This eliminates lany possibility that the waveform of these voltageswill be undesrably deformed in the coupling circuit, such as frequently occurs when the cathode ray tube is coupled to the sawtooth generating circuit by some inductive member such as a transformer. In the latter case, high-frequency oscillations, or transients, often result in vertical bars being visible o-n one side of the image raster due to ringing of the transformer following each retrace interval. Furthermore, transformer :coupling requires very critical adjustment in order to obtain fidelity of image reproduction.

One object of the present invention, therefore,

is to provide an improved form of cathode rayv deiiection circuit of the electrostatic type.

Another object of the present invention is to provide an electrostatic cathode ray beam deflectiony circuit adapted to produce deecting potentials which are balanced with respect to a predetermined voltage level, and which at the same time have peak-to-peak amplitudes which are greater than the maximum value of the supply voltage source.

An additional object of the invention is to provide a single-tube cathode ray beam deflection circuit of the electrostatic type, and further to provide a pair of parallel resonant networks which are respectively connected in the anode and cathode circuits of the tube in such a manner that the energy developed across each such resonant network during the retrace period of the cathode ray beam is made available lduring the succeeding scanning interval to reinforce, or .boost, the potential which would otherwise be developed for deiiecting purposes as a result of the charging of the network capacitance from the operating potential source.

, A still further object of the invention is to provide an electrostatic cathode ray beam .deection circuit including a single discharge tube having a pair of parallel resonant circuits respectively associated with its anode and its cathode, the natural period of oscillation of these resonant circuits being so chosen that the energy developed thereacross during the time that the discharge tube is conductive is utilized during the time that the discharge tube is non-conductive to increase the angle through which the scanning beam of the cathode ray tube is deflected with respect to the angle through which it would normally be deiiected as a result of utilizing only the voltage supplied by the source of operating potential.

Other objects and advantages will be apparent from the following description of preferred forms of the invention and from the drawing, in which:

Fig. l is a circuit diagram of a preferred form of cathode ray beam deflection circuit in accordance with the present invention;

Fig. 2 shows the waveform of the sawtooth Voltage present on one'of the deflecting plates of the cathode ray tube of Fig. 1; and

Fig.v3 is a circuit diagram of a modification of the arrangement shown in Fig. 1.

Referring first to Fig. 1, there is shown a cathode ray beam deection circuit including an electron discharge tube V which is provided with an anode, a cathode and at least one control electrode. This tube V is adapted to control the generation of scanning potentials in a manner now to be set forth, these potentials being respectively applied to a pair of horizontal, or line, deflecting plates H forming part of the deiiecting assembly of an image-reproducing cathode ray tube. The latter also includes the usual means for developing a beam of scanning electrons, which are then deflected by the plates H so as to form a trace on the screen of the tube. It will be further understood that the cathode ray tube is provided with an additional pair 0f deflecting plates or other means for producing a movement of the scanning beam in a direction perpendicular to that produced by the plates H.

However, this second deflection means forms no part of the present invention, and hence an illustration thereof has been omitted from the drawing for the sake of simplicity.

Tube V is designed to control the production of two cyclically varying voltages of sawtooth waveform and opposite phase. Consequently, the tube must be rendered alternately conductive and non-conductive at a rate of 15,750 cycles per second if the developed voltages are to be suitable for a horizontal, or line, deflection of the scanning beam under present television standards. In order to permit the tube to operate in this manner, certain of the components of Fig. 1 are arranged in the form of a blocking oscillator.

A transformer T is included in the anode-cathode circuit of tube V so that the current flowing in this circuit will also flow through one winding of the transformer. The remaining winding of the transformer T has one of its ends connected directly to the control electrode of tube V, as illustrated, and its other end connected to one plate of a capacitor Cg. l

. Accordingly, when tubeV conducts, its grid, or control electrode, becomes initially strongly positive due to the voltage developed across the grid winding of transformer T by the ow of current in the anode-cathode circuit of the tube. This initially positive condition of the grid causes a heavy flow of grid current to charge the capacitor Cg with a negative charge. This is effective to bias the tube V beyond cut-off. It remains non-conductive until the negative charge on capacitor Cg leaks off through the parallel acores? resistor Rig', and the cute-oft levelr of the tube' is again reached. The above operation may? be termed afsquegging" action.

The4 precise instant at which tubel V becomes conductive in each cycle of operation' is controlled by the reception of one' of a series of synchronizing. pulses P on the control electrode of the tube. These pulses P may represent the horizontal synchronizing pulses which form part of a cornposite television signal. However,vv although the circuit of Fig. 1 is being described in connection with the horizontalfdeilecting portion of a television receiving` system, nevertheless it V will be apparent as the description proceeds that the disclosed circuit is also suitable for bringing about a vertical, or field, deection of the electron scanning beam in television circuits or even vfor use s other than in connection with television, such, for example, as in oscillographic work.

The anode of tubeV is supplied with a positive operating potential from a suitable source v(indicated in the drawing as B'|`-) .through the potentiometer R` and an inductorV L1. A by-p'ass condenser C is connected between the movable element of potentiometer R and ground.

A further capacitor C1 is connected between ground and the anode of tube V in a manner such that it is eiectively in parallel relation with the inductor L1, the impedance of the by-pass condenser C being smallvat the operating frequency of the system. rIlhusv the capacitor C1 forms with the inductor L1 a parallel-tuned, or resonant, circuit. As will be brought out in detail below',l the charge developed on this capacitor C1 during operation of the system has a waveform whichis of the substantially sawtooth nature indicated by the reference character S1, with a long ank, or upstr'oke, of the savvtooth extending in a positive direction. This cyclically varying Voltage S1 is applied to one of thev deectng plates H of the cathode ray tube through a wave-shaping resistor R1 and a blocking capacitor Ca.

The plate of the grid capacitor Cg whichv is opposite to that on which the negative charge is developed by' the flow of grid current in tube V is connected to ground and also to the negative terminal of the operating potential source through the parallel combination of a further capacitorv C2 and a furtherv inducftor Le, so that LzCz forms a second parallel-resonant network which isv effectively located in the cathode circuit of tube V. As will be later `brought out', the charge developed on condenser C2 during operation of the system is also of Sawtooth conflguration, but is opposite in phasey to the* sawtooth voltage Si developed on capacitor C1. This? charge on condenser C2', which isi identified by the reference" character S2,A is' symmetrical with respect to the voltage Si, with its vlong flank extending in a negative' direction. The cyclically varying voltage S2 is applied to the remaining plate H of the cathode ray tube throughl a further wave-shaping resistor' R2 andav further blocking capacitor C4.

In order that the deflecting plates H- of the cathode ray tube be operated at a potential which precludes a defocusing of the scanning beani as itA passes between the plates, the latter are connected to the same source of high voltage which serves as the second anode potentialof the cathode ray tube. Due' tothe blocking ca-VA pacitors C and C4', however, the high voltage is prevented from being applied directly to the electrodesof the oscillator tube V.

describing the' operation of the circuit; illus-jf traced in Fig. i., rer it first be that tte V isv rendered conductive byv` the receptionV oi one of. the synchronizing pulses P on the cntol elec# trode thereof. As previously broughtV out; th resulting flow of. anode-cathode current resul-ts. in a strongly positive, charge being.' developed. on the grid of the tube, which. in turnr resul-ts in a sudden surge or grid current to' charge capacitor Gg negatively and cut oirthetube.;

IIhe instant at which one of the synchroni'iingy pulses P is received by tube V is identified as 1 inv Figs. l and 2. As soon: as tubel V cc'nductsv at this time t1, it forms a. loweimpedanc'e path. bei tween condenser Cr and condenser G2. Sin'e there is a charge prsentoir condenser' Cr at this time t1 (as will later be shown); the conduction of tube V effectively resultsl in substantially all of this charge beingl transferred to condenser Gr due inpart to the socalled flywheel effect" of the' resonant circuit Lieu The potentialion. condenser Ci is thus increased by an amount equal to' that by' which thel potential on condenser Gi is decreased. This charge transfer is completed before tubeA V is again cutoff at tiine te (Fig. 2li, the ii'rtervall tie-t2 corresponding to the retrace period of thev cathode ray scanning beam;

At the end of the' retrace interval (or inv other Words; at the time te) the Shimtig aotlo of tube V is terminated, and capacitorCr begli-iste charge from the positive potential source B+ thougntiie potentiometer R and the induct'oi:` L1'. Normally, the voltage to which condenser Ci is charged will have a maximum value which is limited to that of the' operating potential sourceB-i. How` ever, in accordance` with applicantfs invention, th'e resonant network. LrCi eters intov oscillation at the instant tz' when tube V is cu'tv oil-, and eur-'- rent begins to flow through Lr into Ci under tli in-uence of the voltage developed. across the reso"-A nant circuit during the conduction interval of tubeV. This current now' is maximum at soin-e point near the voltage value of but: continues due' to the resonance phenomenon until a peak value is reached at a time equivalent to approximately one-half cycl'eof the peiiod: of LiCi.- Fig?. 2i illustrates. how` osbillatory actionv ofthe resonant circuit LiCi commences at time te. and. re*- sults in the sawtootrr voltage wave Si. on capacitor C1 rising to a level which is considerably in ex#- cess ofthe voltage Es representing the voltage'y of the operating potential source B+. 1 y

In order for the above action to beeifee-tive, however; it is I'ieces'sar'y'A that; the resonant tre# quency of the tuned circuit LiCi be properly shoe sen with respect to the frequency of the synchronizing pulses P; It has beenfound in pracV tice that the described results will be achieved if the network LiCr is tuned toi al frequency such that the' line-'scanning period tzr-wis; of each de-Y ection' cyclev is equally approximately to between one-quarter and one-half the period of oscilla; tion of LiCi. y

Ant the instant tzwhen` tube V is rendered vnoncohd'uctive, the capacitor C2'y in its; cathode circuit (which has acquired the energy present incapaci; tor Ci atthe end of the scanning interval) now begins to discharge' to groundthroughthe i-nduc`v tor L2. However,v due to the' factthatnthe inductor L2 and capacitor C2 aretunedto a frequeri cy of oscillation whichl is substantially identical tothe resonant frequency of L1C1, the flow of,l ourrent through inductor La following cutoffof tube V (or in' other Wordsf the discharge curve of Gz)` has a waveformV Sz" whichl is substantiallythe res versent thewaveformiss` showxr in'Figf; 2 `.v K ,y

ascissa" 'it has been statedlthatthe vonage deveIoped-on condenser'C1 is applied to one of the deilecting plates-.H throughthe resistor R1' and the capacitor C3. In a similar manner; the voltage developed. oncondenser C2 is applied to the remainingy one'of thek plates H through Ythev resistor R2 and the capacitor C4.

It has been found that the resistors R1 and R2 may act respectively to" linearize the deflecting voltages by acting ras wave-shaping units in com- `binationwith the Adistributed capacitances to ,ground ofthe 'deflecting plates H (these capacitances being shown by broken lines in the drawing). l In other words, the presence of the resist- `ors' R1 and R2 permits the phase'of each deflectin'g voltage to be shifted within suiiiciently broad limits so that thel actual potentials as they appear on the delecting plates H may be adjusted for 'substantially perfect balance and linearity.

The natural'period of oscillation of the resonant circuits L1C1 and L2Czwould normally cause an oscillatory current to flow in each of these circuits, as indicated by the broken line in Fig. 2. However, it will be appreciatedl that at the end of the scanning period, or in other words at the time t3, tube V is rendered conductive so as to place avery low resistance across each of the inductors L1 and L2 and thus eieotively terminate the oscillations in the resonant networks. As a result of this mode of operation, each of the circuits L1C1 and YLzCz is effectively permitted to go into oscillation'atthe beginning of each line-scanning interval, but is only allowed to resonate until the beginning of retrace time, or in other words until tube V again vbecomes conductive. Accordingly, the low-frequency of resonance of these tuned circuits does not, undesirablylengthen the retrace time of the cathode ray scanning beam, since the damping action of tube V is so elective that it reduces the amplitude of the oscillations substantially to zero before the instant that a new scanning.' cycle is initiated.

' In Fig. 3 is shown a modification of the deflection circuit of Fig. l in which an additional electron discharge tube is employed. Whereas in Fig. l the tubeV included in its anode-cathode circuit the inductance-capacitance combination LzCz, the circuit of Fig. 3 is so arranged that the cathode of the. tube V is connected directly to ground through one winding of the transformer T. Also, that plate of the grid capacitor Cg which'is opposite'to the one on which the negative charge is developed by the flow of grid current is likewise-connected directly to ground instead of through the same inductance-capacitance combination LzCz. Accordingly, when the tube V-conducts during the retrace interval ifi-t2, thecapacitor C1 in the anodecircuit of the tube V is discharged directly to ground instead of into thec'apacitor C2 as is the case in the circuit oi Fig. l.

A sawtooth potential is developed on condenser 'Grin the circuit of Fig. 3 which is similar to that developed in vthe circuit previously set forth. However, in the circuit of Fig. 3, an additional capacitor Cs is connected between capacitor Ci and ground. The value of these two series-connected'capacitors Ci-and C5 is so chosen that their total capacitance lis substantially equal to that of capacitor C1 in Fig. l. Hence these two elements merely serve asa voltage-dividing network for a purpose now to be described.

The voltage appearing on capacitor C5, which has avwave'form similar to that of the voltage wave Si in Fig. Z'but which is-reduced in amplitude with respect thereto, is applied tov the dond trol electrode of a further electron discharge device V1, which may, if desired, be similar to tube V.v As shown in Fig 3, the cathode of this additional tube V1 is grounded, while its anode is connected through inductor Lz and a further potentiometer Rc to the same source of positive operating potential (B+) as that to which the potentiometer R is connected.

It will now be see'n that this additional tube V1 acts to invert the phase of the voltage Variation Si appearing on its control electrode so as to develop in its anode circuit a voltage variation which will be opposite in phase to the voltage variation S1, and which accordingly will have sub'- stantially the configuration of the voltage wave S2 illustrated in Fig. 1. In order that this voltage wave produced by tube V1 be of an amplitude which is equal to that of the voltage wave p roduced by the tube V, the two potentiometers R and R3 are ganged together so that they may be Aadjusted simultaneously.

It will be noted that, in the circuit of Fig. 3, the capacitor C2 is shown in broken lines. This is due to the fact that in actual practice the in ductor Le may be made to resonate with the distributed circuit capacitance, thus providing an output oscillation suitable for optimum deilection of the cathode ray beam. Hence, it may not be necessary to employ a physical capacitor in the resonant circuit LzCz in Fig. 3, although such a capacitor may of course be used if it is found desirable. However, the circuit LzCz should preferably have a frequency of resonance such that one-half cycle of oscillation of the circuit will occur within the retrace time interval :f1-t2.

Inasmuch as the circuit of Fig. 3 employs an additional electron discharge tube, it develops a substantially increased power output over the maximum voltage which is obtainable with the circuit of Fig. l. However, the latter circuit is especially suitable for providing electrostatic deflection of the cathode ray beam of an imagereproducing tube in television systems where voltages are required which do not exceed, for example, the values given in the following table. In this connection, it has been found advantageous to employ, for maximum efficiency of operation, a tube of a type having a high transconductance. One tube especially suitable is a 6J6 with its two halves connected in parallel.

It is also desirable that the inductors L1 and Le be provided with iron cores to reduce the A.C..re sistance of the resonant circuits and raise their Q. It has furthermore been found in many cases that, unless such iron cores are used, highfrequency oscillations may appear in the voltage waveforms S1 and S2. When iron cores are used, however, the coupling between turns of the inductors is so tight that the magnitude of any such oscillations which may be developed is not great enough to be objectionable. l

The following table illustrates the manner in which the output voltages developed by a system constructed in accordance with the present invention compare with the output voltages 0btainable from those deilection systems of the prior art which are limited to the maximum value of the operating potential source. It will be seen that the peak-to-peak voltage obtainable on each deection plate of the cathode ray tube is increased by the use of applicants circuit as shown in Fig. 1 up to approximately 30% over the'potential of the B+ supply, and by the vuse ofthe atenas# circuit of Fig. 3 up to 'approximately 70% Over the B+ imtential:v

eek-to-pcak pak'to'peak D.C.supp1y p voltage (bozglflcb (one plate) plates) CIRCUIT F FIG 1 USING% 616 CIRCUIT OF FIG. l USING 6J6 WITH BOTH SECTIONS IN PARALLEL CIRCUIT OF FIG. 3 USING B 6N7(V) AND 6C(V1) Having thus described my invention, I claim:

1. In an electrostatic cathode ray beam deflection circuit of the blocking oscillator type, including an electron discharge tube'having an anode, a cathode and at least one control electrode, a source of operating potential 4for said tube, a source of synchronizing pulses of predetermined frequency, and a circuit for applying said synchronizing pulses to the control electrode of Said tube to cyclically initiate the conduction .of the latter, the improvement which comprises a pair of parallel inductance-capacitance networks tuned to resonance at a frequency lower than that of the said synchronizing pulses, means for connecting one of the said resonant networks in the anode circuit of said tube and the other of the said networks in the cathode circuit thereof, whereby the potential cyclically developed across the capacitance in each of the said resonant networks is of substantially sawtooth waveform and has a peak-to-peak value which exceeds thatof the said operating potential source, and means for applying the potentials thus developed in the two resonant networks to control one direction of deflection of the said cathode ray beam.

2. The combination of claim 1, in which each of the two said inductance-capacitance networks has a resonant frequency of between one-quarter and one-half the repetition frequency of the said synchronizing pulses.

3. The combination of claim 1, in which the means for applying the potentials developed in the two said resonant networks to control one direction of deection of the cathode ray beam includes a pair of wave-shaping resistors respectively located between each resonant network and that particular deecting plateof the cathode ray tube to which it is connected, said waveshaping resistors acting, together with the distributed capacitance in the circuit, as phaseshifting units which are effective to compensate at least in part for nonlinearities in the long flank of each cycle of the substantially sawtooth voltages developed in the said resonant networks.

4. In a cathode ray beam deflection circuit ofthe type including an electrostatically deected cathode ray tube, an oscillator tube having an anode, a cathode, and at least one control electrode, a source of operating potential'for the said oscillator tube, a source of synchronizing pulses ci predetermined frequency, and means for applying said synchronizing pulses to the control eiectrodeofvsa'id oscillator tube tofevciicaiiyfilrcillator tube is conductiveand utilizing this en-" ergy duringthe fnext A time-interval when rthe tube is'non-conductive'toincreasethe angle of deec'- tion in one direction -oi :the 'fsad cathode-ray" beam,said improvement lincluding a pair of parallel-tuned inductance-capacitance means for connecting one of the said networks in the anode circuit of said oscillator tube and the other of the said networks in the cathode circuit of said oscillator tube, whereby the potential cyclically developed across the capacitance in each of the said tuned networks is of substantially sawtooth waveform and has a peak-to-peak value which is greater than that of the said operating potential source, and means for respectively applying the potentials thus developed in the said tuned networks to one set of deecting plates in the said cathode ray tube.

5. In combination, an electron discharge tube having an anode, a cathode and at least one control electrode, a source of operating potential for said tube, means for rendering said tube alternately conductive and non-conductive at regularly recurring intervals, a rst resonant inductance-capacitance network, means for connecting said first inductance-capacitance network in the anode circuit of said tube so that the capacitance in said network is charged from said operating potential source through the network inductance when said tube is non-conductive, a second resonant inductance-capacitance network, and means for connecting said second inductancecapacitance network in the cathode circuit of said tube so that when the latter becomes conductive the charge developed on the capacitance of said first inductance-capacitance network during the preceding period when the said tube was non-conductive is transferred to the capacitance of said second network, from which it is gradually dissipated through its associated inductance concurrently with the charging of the capacitance of said rst network, whereby cyclically varying voltages of substantially symmetrical waveform and opposite phase are produced on the respective capacitances of the two said networks.

6. The combination of claim 5, in which the frequency of resonance of the said rst inductance-capacitance network is so chosen that the peak-to-peak charge developed on the capacitance thereof during each interval that the said electron discharge tube is non-conductive exceeds the maximum value of the said operating potential source.

7. In combination, an electrostatically-deiiected cathode ray tube, an electron discharge tube including an anode and at least one control electrode, a source of operating potential for said electron discharge tube, a source of synchronizing pulses of predetermined frequency, a circuit for applying said synchronizing pulses to the control electrode of saidKV electron discharge tube to cyclically initiate theconduction of the latter, a resonant network tuned to a frequency which is lower than the recurrence frequency of the said synchronizing pulses, means for connecting said resonant network in the anode circuit of said electron discharge tube so that the energy cyclically developed in said network is of substantially sawtooth waveform and has a peak-to-peak value which exceeds the voltage of the said operating networks,

l1 potential source, means for deriving from the l REFERENCES GCITEDv energy thus developed in said network a. further l y energy variation which is of symmetrical wavelhoef ftgvgtgergerens are of record m the form with respect to the said rst `energy variation but substantially opposite in phase thereto, 5 UNITED STATES PATENTS and means for respectively applying the two en- Number Name Date ergy variations thus developed to one set of de- 2 421 312 Bobb May 27 1947 meting Plates in Sad cathfde my tubev 214392324 Walke- Apr. s: 194s WILLIAM A.4 STEWART. 2,471,246 Smith May 24, 1949 

